ThirtyFive 21

I have three trucks that we had conducted repairs on but each truck will not drive while in high on the trasfer case. They will drive in high lock and low.

Since it will go into HL and Low it sounds like your linkage is correct.
Sounds like it will only drive with front wheels.
Put it on jack stands(all wheels off ground). When in High the back wheels should be the only thing turning with force. Usually most turn but you can stop all except at least one tire on the back. Have some Marines hold the tires and see if one will continue to spin(you might need to give a little throttle). Also note the rear drive shaft as well. When in HL one front and one back should turn. Low the same thing. Check to see if the rear drive shaft is turning or can be stopped. If it can it is probably the transfer. If it is turning and can't be stopped rear diff really bad. Diffs usually cease but it may be so bad that power is going in but not coming out to wheels.

What repairs were done to the trucks?

One engine replacement, one transmission replacement and one tranfer case speedo cable port repair.

The linkage is probably out of alignment. Disconnect and manually shift it into High and drive around. See if it does then adjust the linkage as needed. I doubt you have three trucks have bad transfers after having been worked on. All three of those require the linkage to be removed. My money is on that.